This invention relates generally to a method for forming extruded plastic pipe, and more particularly to a method for forming pipe of an improved construction.
Plastic pipe has found a variety of uses especially relating to drainage. One of the concerns in the manufacture of plastic pipe is the amount of raw materials consumed and the resultant weight of the finished product. For example, 48" interior diameter solid wall plastic pipe weighs approximately 200 lbs per foot. It has recently been discovered that plastic pipe having apertures formed therein, when the pipe is viewed in cross-section, weighs approximately 30 lbs per linear foot. However, a problem exists in manufacturing pipe having the desired cross-section.
In general, extruded plastic pipe is formed on a production line having a variety of specific machines incorporated into the manufacturing process. One of the first machines is an extruder. Plastic powder, or more preferably pellets, is fed through the extruder where it is subjected to high temperatures such that the plastic melts. The plasticized plastic then proceeds through a feed tube, at the end of which the plastic enters into a typically drum shaped die. At the front of the die is the specific cross-section profile to be extruded. As the hot plastic comes out of the die, it passes over what are called calibrating or calibration fingers or bullets which assist in maintaining the desired cross-sectional form which has been extruded. These calibration fingers are part of a manifold assembly. The rest of the manifold assembly extends from above the die as well as beyond the calibration fingers. In addition to the extruder and die, which is supported on a die post assembly, plastic pipe is manufactured using a former or forming head.
The prior art of pipe manufacture has been unable to fabricate plastic pipe which, in addition to being aesthetically pleasing, has a cross-section which incorporates apertures. Although patents have disclosed inventions in pipe having apertures incorporated therein when the pipe is viewed in cross-section, as a practical matter the pipe has apparently been unable to have been manufactured. Instead, upon flowing through the die head, the hot plastic collapses upon the apertures intended to be formed therein. Additionally, another problem in trying to manufacture plastic pipe having such a cross-section is that the hot plastic has tended to clog as it exits the die head and starts to flow over the bullets. It is thus apparent that the need exists for a method for manufacturing an aesthetically pleasing product having the desired cross-section.